The National Security Council has served as an advisory board for American presidents on all matters related to national security and foreign policy since it was created in 1947.

The national security adviser generally serves as chair during meetings of the council not attended by the president and is supposed to be an objective arbiter for the commander-in-chief.

Late Monday, Michael Flynn resigned as national security adviser after it came to light he misled the administration about conversations he held with Russia’s ambassador during the presidential transition process.

President Donald Trump has since named retired Lt. Gen. Keith Kellogg as the acting national security adviser.

Prior to being named to the job, Flynn held a similar role as Trump’s go-to national security adviser during the campaign and was the only military figure of his rank and stature to support Trump throughout the election.

Retired U.S. Vice Admiral Robert Harward, a former Navy SEAL, was offered the position after Flynn's resignation, but turned it down, citing personal issues.

Harward told the Associated Press the Trump administration was “very accommodating” to him but he turned down the offer because he is “in a unique position finally after being in the military for 40 years to enjoy some personal time.”

Each president is given wide latitude to organize and use the NSC. Some presidents have chosen to employ large NSC staffs and rely on them heavily, while others have employed small staffs and used them only occasionally.

When he took office, Barack Obama dismantled the White House Homeland Security Council created by former President George Bush in the aftermath of the September 11 attacks in 2001 and folded its responsibilities in with those of the NSC.

At the time, Obama’s national security adviser, Gen. James L. Jones, said the change would “allow the president to make better decisions even more rapidly.”

When Trump took office, he made several changes to the structure of the NSC’s Principals Committee, which comprises the highest-ranking members of the full council.

Trump gave his chief strategist, Steve Bannon, a permanent invitation to the meetings, and allows his Chairman of the Joint Chiefs of Staff and Director of National Intelligence to attend meetings only when issues arise that pertain to them.

Controversy

Flynn became embroiled in controversy last week when The Washington Post reported he spoke to Russian Ambassador Sergey Kislyak about sanctions placed on Russia, despite repeatedly denying the conversations took place.

National Security Adviser Michael Flynn in the east Room of the White House in Washington, Feb. 13, 2017.

The discussions raised concerns he may have offered the Russians some kind of assurances that the Trump administration would lift the sanctions placed on Russia by the Obama administration. Those conversations would mark a possible violation of the Logan Act, which forbids unauthorized citizens from conducting diplomacy on behalf of the U.S.

Flynn isn’t the first national security adviser to resign after facing scandal.

President Ronald Reagan had two advisers step down after being convicted for connections to the Iran-Contra affair, which involved several administration officials conspiring to illegally funnel profits from arms sales to Iran to the Contras militant group in Nicaragua.

Robert McFarlane served as national security adviser for slightly more than two years when he resigned in 1985 for what he called personal reasons. He later pleaded guilty to withholding information from Congress in an attempt to cover up the arms sales.

His replacement, John Poindexter, also played a role in the Iran-Contra affair, and in 1986, also resigned after serving less than a year. He later was found guilty in connection to the scandal, but appealed the decision and had it overturned.